observer.php

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<?php
/**
* @version		$Id:observer.php 6961 2007-03-15 16:06:53Z tcp $
* @package		Joomla.Framework
* @subpackage	Base
* @copyright	Copyright (C) 2005 - 2008 Open Source Matters. All rights reserved.
* @license		GNU/GPL, see LICENSE.php
* Joomla! is free software. This version may have been modified pursuant
* to the GNU General Public License, and as distributed it includes or
* is derivative of works licensed under the GNU General Public License or
* other free or open source software licenses.
* See COPYRIGHT.php for copyright notices and details.
*/

// Check to ensure this file is within the rest of the framework
defined('JPATH_BASE') or die();

/**
 * Abstract observer class to implement the observer design pattern
 *
 * @abstract
 * @subpackage	Base
 * @since		1.5
 */
class JObserver extends JObject
{

	/**
	 * Event object to observe
	 *
	 * @access private
	 * @var object
	 */
	var $_subject = null;

	/**
	 * Constructor
	 */
	function __construct(& $subject)
	{
		// Register the observer ($this) so we can be notified
		$subject->attach($this);

		// Set the subject to observe
		$this->_subject = & $subject;
	}

	/**
	 * Method to update the state of observable objects
	 *
	 * @abstract Implement in child classes
	 * @access public
	 * @return mixed
	 */
	function update() {
		return JError::raiseError('9', 'JObserver::update: Method not implemented', 'This method should be implemented in a child class');
	}
}